Foundry cores are used to make objects of particular shapes in melting processes. For example, foundry cores can be adopted in melting processes for making perforated metal objects.
Foundry cores are usually made with particular sands for cores, for example so-called “pre-coated” sands, i.e. sands that are dipped in suitable liquid resins so that, when the resin dries out, it covers the initial grains of sand. In order to make the core, the pre-coated sands are suitably worked through specific treatments so as to give the finished core the desired shape and an adequate compactness.
A typical process for forming foundry cores foresees their formation in moulds. Such moulds, usually comprising a first and second half-mould, are provided with one or more core forms, i.e. cavities formed in the moulds having a shape corresponding to the final shape that the core must have. The core forms are connected together by conveying channels through which the sand is inserted inside the preheated mould and conveyed so as to fill all of the core forms. The contact between the walls of the preheated mould and the sand ensures that the resin with which the latter is coated reaches a firing temperature, so as to solidify, compacting the sand. The cores are then removed from the moulds and subjected to precision processing, in particular trimming.
Such equipment for forming cores according to the prior art is not however without drawbacks.
Of course, the solidification of the sand in the mould does not only involve the area of the core forms, but also the areas of the conveying channels. Therefore, what is removed from the mould at the end of the forming process are not separate cores, but rather clusters of cores connected together by further solid parts, corresponding to the conveying channels, in the case in which many core forms are foreseen in the mould, or else a single core to which a solid part is connected corresponding to the injection channel in the case in which a single core form is foreseen in the mould. Such solid parts are commonly known as “burrs”. Before proceeding with the precision processing of each of the cores, it is thus necessary to remove the burrs through suitable operations, typically cutting. Such burr removal operations involve an overall lengthening of the core processing cycle.
A further drawback of the described equipment is the waste of sand for cores that forms the burrs, which means a worsening of the overall processing costs of the cores.